Amorphous Carbon Research Articles

Carbon nanostructures synthesis by catalyst-free atmospheric pressure plasma jet

In this study, carbon nanostructures were synthesized utilizing a warm plasma jet at atmospheric pressure in a continuous and catalyst-free process. The procedure and apparatus were designed and constructed in our laboratory. Plasma was generated with 600 W of electrical energy, using a high-voltage, high-frequency alternating current power source. The working gas utilized was a propane/butane mixture, with a concentration ratio of 60:40, respectively. A production rate of 300 mg min−1 of powdered material was achieved, with a particle size between 20 and 100 nm. The product was characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, Raman spectroscopy, x-ray diffraction, and transmission electron microscopy. Results show the formation of multilayer carbon nanostructures with a low content of functional groups; the obtained material presented structural defects and amorphous carbon. This work demonstrates that, with adequate control, warm plasma jet discharges can be employed for the synthesis of carbon nanostructures. The process is scalable and can be utilized for hydrocarbon reforming and hydrogen production. However, further studies are needed to improve the quality of the nanostructures and process efficiency. The synthesized material can potentially be used in gas adsorption or in the manufacture of polymeric nanocomposites with enhanced thermal, electrical, and mechanical properties.

Macroscale Superlubricity with High Pressure Enabled by Partially Oxidized Violet Phosphorus for Engineering Steel

AbstractAs a novel cross‐structured 2D material, violet phosphorus (VP) promises to further develop the dynamic performance, energy efficiency, and service lifetime of mechanical components owing to its high strength and toughness, large carrier mobility, wide bandgap, and good friction‐reducing properties. In this work, the partially oxidized violet phosphorus nanosheets (oVP) are synthesized and employed as the lubricating additives in the poly alpha olefin (PAO) oil environment with less oleic acid (OA) improver, which can trigger the macroscale superlubricity on the diamond‐like carbon (DLC) film deposited steel surface at high loading pressures (>800 MPa) and sliding speeds (>0.1 m s−1). The friction coefficient (COF) of the steel‐DLC tribopair lubricated by the oVP‐PAO oil can reduce down to 0.0064 with little wear. At the high‐pressure sliding interface, the force‐thermal coupling action during the running‐in process promotes the cleavage and recombination of oVP nanosheets and OA molecules to form a reliable chemical adsorption tribofilm mainly composed of phosphorus oxides and amorphous carbon, which prevents the original asperities from direct contact and provides an ultralow shear strength. These findings suggest a new method to achieve macroscale oil‐based high‐pressure superlubricity for engineering steel through the lubrication and catalyzation effects of oVP.

Effect of temperature on the ability to synthesize SiC from rice husks

Abstract Agricultural production in Vietnam annually generates a substantial volume of by-products and waste, with rice husks constituting the predominant fraction. Due to their meager economic value, rice husks are typically deemed agricultural waste and are commonly disposed of through incineration or discharge into rivers, contributing significantly to environmental pollution. In this investigation, rice husks were employed as the principal raw material for synthesizing silicon carbide. A blend of rice husks and silica gel in a ratio of 1.4/1 was subjected to sintering in a CO2 environment within the temperature range of 800 – 1200 oC for 30 minutes. The chemical composition of the resultant product post-pyrolysis was ascertained in accordance with the ISO 21068-2:2008 standard. The capacity for SiC formation was further assessed utilizing Fourier transform infrared spectroscopy and X-ray diffraction. The outcomes revealed that the optimal temperature for SiC synthesis was 1200 oC. The composition of the sample post-pyrolysis was determined as 20.4% SiC, 51.2% SiO2, and 26.4% C (%wt.). The primary phase constituents encompass amorphous carbon, cristobalite, α-SiC, and β-SiC. Scanning Electron Microscopy/ Energy Dispersive X-ray imaging of the product at 1200 oC exhibited dispersed SiC crystals on a SiO2-C substrate. The presence of SiC suggests the potential application of the product as a wear-resistant material.

Amorphous nitrogen-doped carbon layers forming the interfacial channel for rapid charge transfer in ZnIn2S4/BiVO4 Z-scheme photocatalyst for enhancing organic pollutants degradation with simultaneous hydrogen evolution

Efficient photocatalytic hydrogen evolution from the organic wastewater represents an ideal solution for simultaneously addressing energy shortages and environmental pollution. However, the sluggish transport of photogenerated carriers at contact interface poses a key obstacle to enhancing photocatalytic activity. Here, ZnIn2S4/BiVO4@N-C (ZIS/BVO@N-C) Z-scheme photocatalysts were successfully constructed by a simple hydrothermal-impregnation method. ZIS/BVO@N-C-10% demonstrated outstanding photocatalytic performance, achieving a hydrogen evolution rate of 2695.68 μmol·g−1·h−1 and a degradation rate of 492.96 mmol·g−1·h−1 under visible light, surpassing those of ZIS (851.52 μmol·g−1·h−1 and 174.83 mmol·g−1·h−1) and ZIS/BVO-10% (1228.98 μmol·g−1·h−1 and 277.78 mmol·g−1·h−1). Characterization results and density functional theory (DFT) calculations revealed that the introduction of the N-C layer reduced interfacial impedance and enhanced the strength of interfacial electric field, overcoming the interfacial barrier and improving the photogenerated separation and migration efficiency at the interface, and ultimately enhancing the photocatalytic activity of ZIS/BVO@N-C. Based on experimental and characterization results, the photocatalytic mechanism of ZIS/BVO@N-C Z-scheme has been proposed. Furthermore, ZIS/BVO@N-C exhibited excellent stability, highlighting its potential for practical applications. This work also presents a new strategy for designing highly active Z-scheme photocatalysts for organic wastewater treatment and simultaneous hydrogen energy recovery.

Temperature-dependent excitonic emission characteristics of highly crystallized carbon nitride nanosheets

Highly-crystallized carbon nitride (HCCN) nanosheets exhibit significant potential for advancements in the field of photoelectric conversion. However, to fully exploit their potential, a thorough understanding of the fundamental excitonic photophysical processes is crucial. Here, the temperature-dependent excitonic photoluminescence (PL) of HCCN nanosheets and amorphous polymeric carbon nitride (PCN) is investigated using steady-state and time-resolved PL spectroscopy. The exciton binding energy of HCCN is determined to be 109.26 meV, lower than that of PCN (207.39 meV), which is attributed to the ordered stacking structure of HCCN with a weaker Coulomb interaction between electrons and holes. As the temperature increases, a noticeable reduction in PL lifetime is observed on both the HCCN and PCN, which is ascribed to the thermal activation of carrier trapping by the enhanced electron–phonon coupling effect. The thermal activation energy of HCCN is determined to be 102.9 meV, close to the value of PCN, due to their same band structures. Through wavelength-dependent PL dynamics analysis, we have identified the PL emission of HCCN as deriving from the transitions: σ*–LP, π*–π, and π*–LP, where the π*–LP transition dominants the emission because of the high excited state density of the LP state. These results demonstrate the impact of high-crystallinity on the excitonic emission of HCCN materials, thereby expanding their potential applications in the field of photoelectric conversion.

Structural and mechanical properties of monolayer amorphous carbon and boron nitride

Structural and mechanical properties of monolayer amorphous carbon and boron nitride

Synthesis of core-shell nanoparticles with liquid core using magnetron sputtering and capacitively coupled dusty plasmas

Abstract We succeeded in depositing amorphous carbon films around tin nanodroplets retained in a capacitively coupled plasma (CCP). High-pressure magnetron sputtering was used for synthesizing tin nanoparticles at the top of a vacuum chamber. Tin nanoparticles were transported to CCP at the bottom of the chamber, and they were trapped in the sheath above an rf electrode. Tin nanoparticles were heated above the melting point by ion bombardment in CCP. We introduced methane into CCP to deposit amorphous carbon films around melted tin nanoparticles. The transmission electron microscope (TEM) images of core-shell nanoparticles showed completely spherical cores. We observed the melting of cores at the melting point of metal tin when we heated core-shell nanoparticles in TEM, suggesting that the amorphous carbon films protected cores from the oxidation. In addition, the amorphous carbon films were robust against the volume expansion of the cores due to melting.

Carbon/C3N4 heterostructures constructed from lignin toward enhanced lithium-ion storage

Lithium-ion batteries (LIBs) are widely used in portable energy storage. The capacity of commercial graphite is difficult to improve due to the stoichiometry limit of LiC6 of graphite, thus new anodes need to be developed to meet the demand of high-energy–density LIB. The growing interest in graphitized carbon nitride (g-C3N4) stems from its structural resemblance to graphite and its capacity to offer abundant adsorption and intercalation sites. However, g-C3N4, as a semiconductor, has a low lithium transfer rate due to its poor conductivity and high diffusion resistance. Improving the electron transport rate of g-C3N4 and reducing the adsorption energy barrier of Li+ in g-C3N4 are the keys to improving the electrochemical performances of g-C3N4. In this study, lignin and melamine were homogeneously mixed using the spray drying method, followed by the preparation of covalently bonded C3N4/LC material through a one-step carbonization process. The uniform dispersion of g-C3N4 in amorphous carbon can improve the conductivity and reduce the diffusion energy barrier of Li+. As a result, the C3N4/LC-x anode has better electrochemical behavior, including higher reversible capacity, better rate performance, and cycle stability.

Bonding structure and dry etching characteristics in amorphous B–C–N films for hardmask applications

The etch selectivity of the hardmask layer in lithography process for semiconductor chip manufacturing is being continually improved through the utilization of single-element introduction in amorphous carbon (a-C) matrix. Because the exploration of ternary hardmask systems is lacking, we analyzed the bonding structure and dry etching characteristics of a hardmask composed of a ternary system by combining Boron (B) and Nitrogen (N), which are widely used in single-element addition in a-C films. Amorphous B–C–N (a-BCN) hardmasks were obtained by adjusting the N content in an amorphous boron-carbon film using the DC sputter process. The differences in N content within the a-BCN hardmask before and after dry etching were characterized through X-ray reflectometry (XRR) and X-ray photoelectron spectroscopy (XPS) analyses. Consequently, an increase in the ratio of B–N and C–N bonds and a decrease in film density were observed in the pre-etched film. Furthermore, we identified that etch selectivity is related to changes in B–C bonds and C–C sp2 bonds in the post-etched residual film. Additionally, density functional theory (DFT) calculations confirmed an increase in the binding energy between C atoms within the film and etchant, F, influenced by N within the film. This revealed that N in ternary systems not only deteriorates physical density, as known from previous binary hardmask research, but also chemically promotes etch reactions. In our paper, we elucidate the aspects regarding the relationship between the etchant F and C that should be considered when designing ternary hardmask systems.

Heterogeneous Ni-Boride/Phosphide Anchored Amorphous B-C Layer for Overall Water Electrocatalysis.

The rational design of efficient and economical bifunctional electrocatalysts remained a challenge for overall water electrolysis. In this work, the Ni-boride/ phosphide particles anchored amorphous B-doped carbon layer with hierarchical porous characteristics in Ni foam (Ni3P/Ni3B/B-C/NF) was fabricated for overall water splitting. The Boroncarbide (B4C) power was filled and fixed in the NF interspace through the electroplating and electroless plating, and then annealed in vacuum high temperature. The amorphous B-C layer derived from the B4 C not only speeded up the electron transport, but also cooperate with Ni-boride/phosphide to enhance the electrocatalytic activity for HER and OER synergistically. Furthermore, the hierarchical porous architecture of Ni3P/Ni3B/B-C/NF increased space utilization to load more active materials. The self-supported Ni3P/Ni3B/B-C/NF electrode possessed a low overpotential of 212 and 280 mV to deliver 100 mA cm-2 for HER and OER, respectively, and high stability for 48 h. In particular, the electrolyzer constituted with the Ni3P/Ni3B/B-C/NF bifunctional electrocatalyst only required a voltage of 1.59 V at 50 mA cm-2 for water electrocatalysis under alkaline medium, and demonstrated long-term stability for 48 h. This study provides a new technical path for the development of bifunctional of transition metal borides to promote the application of hydrogen production from water splitting.

Investigating different carbon-based target materials: Can we improve ionization in HiPIMS for the deposition of diamondlike carbon films?

Investigating different carbon-based target materials: Can we improve ionization in HiPIMS for the deposition of diamondlike carbon films?

Dense Al2O3 sealing inhibited high hydrostatic pressure corrosion of Cr/GLC coating

The corrosion failure of amorphous carbon (a-C) coatings is commonly ascribed to the existence of growth microdefects, which serve as pathways for corrosive fluids to permeate the substrate. Atomic layer deposition (ALD) is renowned for its ability to augment the corrosion resistance of metallic materials. Graphite-like carbon (GLC) is one of the amorphous carbon materials dominated by hybridized sp2-C bonds. In this study, an ALD-deposited Al2O3 layer is specially introduced on the Cr/GLC multilayer coating to solve the aforementioned corrosion risk of a-C by taking the sealing conception for defects. Compared to the as-deposited Cr/GLC coating, the coating encapsulated with Al2O3 layer depicts the reduction of corrosion current density over two orders of magnitude under a wide pressure range of 0.1 ~ 15 MPa. Particularly, the presence of released Crn+ and Fen+ in the corrosion solution is significantly diminished, accompanying with a small quantity of Aln+ generated in sealed coating during corrosion. Microstructural analysis and electrochemical results identified that both the dense Al2O3 layer offered strong safeguard for Cr elements released from multilayers, whilst amorphous carbon network inhibited the likelihood chloride penetration induced by partially infiltrated Al2O3, which made the synergistic contributions to the enhancement of corrosion resistance for Cr/GLC coating for deep-sea applications.

Highly efficient peanut shell activated carbon via hydrothermal carbonization and chemical activation for energy storage applications

In this study, the activated carbon samples from peanut shells (PS) are synthesized through hydrothermal carbonization (HTC) with and without activating agents, and their electrochemical properties are studied for supercapacitor applications. The raw precursor (PS) powder is loaded with an activating agent (ZnCl2 or H3PO4 or KOH) during the hydrothermal treatment at 200 °C for 7 h. The treatment with the activating agent facilitates the generation of oxygen-containing functional groups on the precursor surface, enhancing the porosity and electrochemical performance of the sample. Further, the samples are subjected to carbonization at 400 °C for 3 h. The powder XRD patterns show peaks at around 24–26° and 43°, corresponding to the amorphous and graphitic carbon, respectively. The morphological examination reveals more meso and macro pores when treated with the activating agent. Raman spectra manifest the amorphous carbon nature of the samples exhibiting ID and IG bands. The porous carbon treated with H3PO4 shows a specific surface area of 17.8 m2/g and a pore volume of 0.037 cm3g−1. The H3PO4 treated sample shows a high specific capacity (Cs) of 240 F/g at 1 A/g current density, an energy density (E) of 4.08 W h kg−1, and a power density (P) of 101.3 W kg−1. The Retention rate of the sample is approximately 90 % up to 1200 cycles. These types of hybrid supercapacitor materials are suitable for battery-type applications.

Novel ion beam implantation of felt electrodes for the vanadium flow battery: Role of defects versus nitrogen groups for the VO2+/VO2+ redox reaction

A novel approach to introduce catalytic sites to carbon and graphite felts in order to improve electrode activity and investigate the effectiveness of specific active sites for the vanadium flow battery (VFB) has been achieved via ion beam implantation. Here, both N2+ and Ne+ implantation is used to show that the positive vanadium (VO2+/VO2+) redox reaction preferentially occurs at the introduced defect sites, and not nitrogen-containing groups. This is shown through short charge and discharge tests and electrochemical impedance spectroscopy, with the electrodes characterised via X-ray photoelectron and Raman spectroscopies. Lower implantation fluences (1 × 1014–4 × 1015 ion cm−2) were shown to improve the pristine electrodes due to the formation of defect sites. However, implantation at higher fluences (above 4 × 1015 ion cm−2) resulted in a decrease in defect density, and a layer of amorphous carbon at the electrode surface was thought to hinder the redox reaction due to lower surface conductivity and less available active sites. This new approach of felt electrode modification shows that nitrogen-containing groups are not necessary for the positive vanadium redox reaction and shows the importance of defect engineering of electrodes for the VFB.

Investigating the effects of silicon and carbon components on the thickness evolution and performance degradation of silicon–carbon electrodes through electrochemical dilatometry

The severe volumetric changes occur during the lithiation/de-lithiation of silicon materials, which are the main cause of battery capacity failure. In this study, the expansion behavior of a cell composed of a silicon-carbon anode and Li(Ni0.5Co0.2Mn0.3)O2 (NCM523) was measured using the electrochemical dilatometry, and the contributions of different silicon and carbon components to the expansion were analyzed, along with factors affecting the cyclic stability of the silicon carbon anode. The results indicate that amorphous carbon can inhibit the volume expansion of monocrystalline silicon in the late stage of lithiation, thereby ensuring the cyclic stability of silicon. The cyclic stability of silicon-carbon composites is affected by irreversible expansion and expansion variation, and these two factors are negatively correlated. This research provides insights and guidance for the design of silicon carbon electrodes with superior electrochemical performance.

Photochemistry of Photoinduced-Reaction Generated Bubbles.

UV light can create and grow bubbles (herein referred to as PIRGBs for photoinduced-reaction generated bubbles) at liquid/solid interfaces through photoinduced reactions that produce gases. Unlike the simple experience of blowing water bubbles through a straw, in which the bubbles quickly move away from their nucleation sites, not only can a deep UV laser beam create PIRGBs in liquid acetone, but also can hold and grow them. Free bubbles could be attracted to the excitation region from millimeters away, indicating that the reactions cause radial inward flow on the liquid surface. The radial flow can be due to imbalanced surface tensions at the interfaces. Raman measurements reveal that the gases in the PIRGBs include C2H6, CO, and H2, and in liquid acetone, sp2-carbon species are detected upon the UV excitation. Time series Raman measurement discloses a photocarbonization process in which small acyclic carbon species gradually form small clusters with carbon rings and eventually produce a large piece of amorphous carbon at the top of a PIRGB in pure liquid acetone. The photocarbonization may open new avenues for development of carbonaceous materials. Using PIRGB, miniature or microscale gas production reactors can be developed for producing gases.

Enhanced Long-Term Corrosion Resistance of 316L Stainless Steel by Multilayer Amorphous Carbon Coatings.

Diamond-like carbon (DLC) coatings are effective in protecting the key components of marine equipment and can greatly improve their short-term performance (1.5~4.5 h). However, the lack of investigation into their long-term (more than 200 h) performance cannot meet the service life requirements of marine equipment. Here, three multilayered DLC coatings, namely Ti/DLC, TiCx/DLC, and Ti-TiCx/DLC, were prepared, and their long-term corrosion resistance was investigated. Results showed that the corrosion current density of all DLC coatings was reduced by 1-2 orders of magnitude compared with bare 316L stainless steel (316Lss). Moreover, under long-term (63 days) immersion in a 3.5 wt.% NaCl solution, all DLC coatings could provide excellent long-term corrosion protection for 316Lss, and Ti-TiCx/DLC depicted the best corrosion resistance; the polarization resistances remained at ~3.0 × 107 Ω·cm2 after immersion for 63 days, with more interfaces to hinder the penetration of the corrosive media. Meanwhile, during neutral salt spray (3000 h), the corrosion resistance of Ti/DLC and TiCx/DLC coatings showed a certain degree of improvement because the insoluble corrosion products at the defects blocked the subsequent corrosion. This study can provide a route to designing amorphous carbon protective coatings for long-term marine applications in different environments.

Nano-silicon embedded in mildly-exfoliated graphite for lithium-ion battery anode materials

Silicon-based materials have a high theoretical specific capacity and a low discharge potential, whereas the significant capacity fading owing to weak conductivity and volume exfoliation effect. The co-utilization of silicon and graphite has become a feasible method for realizing high-performance lithium-ion batteries (LIBs). Herein, the C@p-Si/ESG composite anode material with “sandwich” structure was obtained by electrostatic assembly of mildly-exfoliated graphite and electrostatic modified nano silicon, and subsequent coated with amorphous carbon on the surface of the material. The carbon coating and the mildly-exfoliated graphite form a buffer space, which alleviates the volume expansion effect of silicon in the process of lithium alloying. In addition, the SEI film is generated outside the carbon layer, reducing the consumption of the electrolyte and the occurrence of side reactions. C@p-Si/ESG exhibits a high charge–discharge rate and an excellent long-term cycle stability.

Origin of the Surface Facet Dependence in the Thermal Degradation of the Diamond (111) and (100) Surfaces in Vacuum Investigated by Machine Learning Molecular Dynamics Simulations

We perform machine learning molecular dynamics simulations to gain an atomic-level understanding of the dependence of the graphitization and thermal degradation behavior of diamond to the (111) and (100) surface facets. The interatomic potential is constructed using graph neural network model, trained using energies and forces from spin-polarized van der Walls-corrected density functional theory calculations. Our results show that the C(111) surface is more susceptible to thermal degradation, which occurs from 2850 K through synchronized bilayer exfoliation mechanism. In comparison, the C(100) surface thermally degrade from a higher temperature of 3680 K through the formation of sp1 carbon chains and amorphous sp2-sp3 carbon network. Due to the dangling bonds at the step edges, the stepped surfaces are more susceptible to thermal degradation compared to the corresponding flat surfaces, with the stepped C(111) and C(100) surfaces thermally degrading from 1810 K and 3070 K, respectively. We propose potential applications of this study in diamond tool wear suppression, diamond polishing, and production of graphene directly from the diamond surface.

Photo-ionization structures of Planetary Nebula IC 2003 with [WR] central star

We present ionization structures of IC 2003, a planetary nebula with [WR] central star, using a 1-D dusty photo-ionization code: ”CLOUDY 17.03”. The photo-ionization model is constrained by archival UV emission line fluxes, medium-resolution optical spectroscopy, IRAS25μm flux, absolute Hβ flux, and the mean angular size of the nearly spherical optical nebula. To constrain the carbon abundance and the effect of photo-electric heating in the ionized gas, we used UV emission lines. We considered an amorphous carbon dust grain with MRN and KMH size distributions to address the importance of photo-electric heating in the ionized nebula. We show that KMH grain size distribution with quantum dust heating reproduces the observations quite well. We construct the ionization structures of different elements at their different ionization stages in the nebula. We derive the physical properties of the planetary nebula and its chemical composition, as well as the parameters of its central star. The estimated nebular dust-to-gas mass ratio is 2.37×10-3, and the enhanced photo-electric heating yielded by small dust grains is 9.4% of the total heating. We considered the H-poor model atmosphere for the central star; the effective temperature of the central star is 177kK, the specific gravity log(g) is 6, and its luminosity (L∗) is 6425 L⊙. The derived central star parameters plotted on stellar evolutionary tracks correspond to a central star mass of 0.636M⊙and to a progenitor mass of 3.26M⊙.